1. Field of the Invention
The present invention relates to a novel polyfunctional peroxide to be utilized as a polymerization initiator for a vinyl monomer, a curing agent and a crosslinking agent for a polymer, a polymerization initiator comprising the same and a process for polymerizing a vinyl monomer employing the same.
2. Description of the Related Art
Polyfunctional peroxides having a plurality of peroxy bonds have conventionally been employed as polymerization initiators, when high molecular weight vinyl polymers are to be obtained by subjecting vinyl monomers to bulk polymerization or suspension polymerization.
Various kinds of compounds are so far known as such polyfunctional peroxides. For example, U.K. Patent No. 1049969 discloses 1,1,4,4-tetra(t-butylperoxy)cyclohexane. Japanese Patent Publication No. Sho 40-19013 discloses 2,2-bis (4,4-di(t-butylperoxy)cyclohexyl)propane. Japanese Patent Publication No. Sho 58-56561 discloses tri(t-butylperoxy)triazine. Japanese Patent Publication No. Hei 1-30844 discloses tri(t-butylperoxy)trimellitate.
However, these conventional polymerization initiators have low polymerization initiation efficiency, so that they have a low probability that all of the peroxy bonds which are present in each molecule act effectively as the polymerization initiator. Accordingly, the conventional polymerization initiators substantially act as the polyfunctional initiators at low rates.
More specifically, polymerization mechanism resorting to a polyfunctional peroxide is supposed to operate usually as follows. First, radicals formed by initial cleavage of some of the peroxy bonds in the polyfunctional peroxide are added to the monomer to initiate polymerization thereof. Thus, a polymer containing peroxy groups is formed. The polymerization initiation efficiency at this initial stage is substantially the same as those of the conventional monofunctional peroxides.
Next, the peroxide moieties in the polymer are decomposed to form polymer radicals, which initiate another polymerization to form a high molecular weight polymer or a branched polymer. However, the conventional polyfunctional peroxides involve a problem that the polymer radicals serving as the polymerization initiator in the second step have low polymerization initiation efficiency. Accordingly, polyfunctional polymerization initiators having higher polymerization initiation efficiency are in demand.